Patent GB-1206003-A (GB)
Title: Improvements in and relating to the resistance-welding of metal sheets coated or covered on at lease one side with an insulating layer
Inventor: BECKER OTTO ALFRED
IPC: B23K11/16
Filed: 1968-01-23
Abstract: 1,206,003. Welding by pressure. O. A. BECKER. 23 Jan., 1968 [11 Feb., 1967; 27 Feb., 1967; 24 April, 1967; 29 July, 1967], No. 3441/68. Heading B3R. In resistance welding metal sheets coated with insulating layers, the insulating material is melted or destroyed by resistance heating in the intended weld area to allow current to pass through the sheets between electrodes to weld the sheets together. Two metal sheets 1, 2, Fig. 1, coated externally with non-metallic layers 1a 2b have metal pieces 14 arranged magnetically or by cement between the sheet inner faces, the ends of the sheets are bared of the layers 1a, 2b and an area 1c of the upper sheet is also bared. The upper electrode 20 is connected by cable 22 to the upper sheet and the lower electrode 21 is connected by cable 23 to the lower sheet, current flow between the electrodes melting the layer 2b and a first weld being made. Further welds are made without removing the layer. Two sheets coated on both sides may be welded by connecting the lower electrode to a bared area of the upper sheet and applying the upper electrode to a bared area over the proposed weld. The metal sheets may be pre-heated. Three metal sheets 1, 2, 3, Fig. 4, with non-metallic layers 1a, 1b, 2a, 2b, 3a, 3b are provided with a connection from the upper electrode to the upper sheet, a connection from the lower electrode to the lower sheet and pin connections 12a, 12b between the first and second sheets 1, 2 and second and third sheets 2, 3. For the first weld an area 1c of the upper layer 1a is removed, for subsequent welds no removal is necessary. In a modification a pair of pins are passed through all the sheets at their ends and these pins are connected respectively to the upper and lower electrodes. For welding four coated sheets a pin is passed through all the sheets at one end and the lower sheet is connected to the upper electrode via a resistor to limit the weld size. Two sound-damping panels, each formed by sheets separated by non- metallic material with one sheet coated on one side with non-metallic material are welded by interconnecting the electrodes to both panels and using metal pieces between the adjacent . bare sheets. Alternatively the lower electrode is connected to the upper panel and vice versa and a large corrugated member is arranged between the adjacent bare sheets. In welding sheets arranged as in Fig. 4, the lower electrode is connected to the upper sheet and to a lowmelting wire beneath the upper electrode. The upper electrode is connected to the lower sheet and to a low-melting wire beneath the lower electrode. On passing current the wires melt and destroy the adjacent non-metallic layer. The coating layers of the upper and lower of three coated sheets 1, 2, 3, Fig. 12 are removed at the weld area and the bared areas are engaged by electrodes 20, 21 surrounded by spring- pressed contact tubes 35 insulated therefrom. The contact tubes are connected by leads 22 containing resistors 25 to the opposite electrodes. Current flows from the upper electrode to upper contact tube 35 to the lower electrode and from the lower electrode to the lower electrode tube to the upper electrode to heat and melt the non-metallic layers. Thelowernon- metallic layer 3b need not be removed. In a modification the contact tubes only are connected. A main electrode with two adjacent auxiliary electrodes insulated therefrom are arranged above and below three coated sheets, the main upper electrode being connected to the lower auxiliary electrodes and vice versa. Current flows from the upper main electrode to the adjacent side electrodes to heat and melt the coating layers. The auxiliary electrodes may be provided in the form of a pair of tongs. A main electrode and an auxiliary electrode, insulated therefrom, are provided on each side of three coated sheets, the auxiliary electrodes being connected electrically and each electrode engaging a bared spot on a sheet. Alternatively two electrodes between which current may flow are arranged on each side of the sheets. An upper electrode 20, Fig. 19, has an annular edge 56 in a water-cooled tip of copper-tungsten alloy carried on a holder 58 and spring-urged towards the work. A hood 63 surrounds the electrode tip and sealingly engages the work, a protective gas being supplied to the hood. A lower electrode with ball-and-socket connected tip 21 is connected to the upper workpiece. The cutting edge penetrates the non- metallic coating on the upper workpiece to establish connection with the electrode. A spring-urged pointed bolt may be provided in the upper electrode to pierce the upper layer and the lower electrode may be connected to a pin pushed into a hollow rivet passing through the sheets. Roller electrodes for seam welding three coated sheets connected at one end by a pin are provided with a cutter disc, sheet metal bodies with pressed-out points or hollow rivets with an annular cutting edge may be pressed through the coatings by the electrodes to establish initial contacts. These bodies may be supplied to the desired spots by means of paper belts carrying the bodies and fed with the sheets to be welded between the electrodes. Alternatively the bodies may be fed from a container down a shoot to a position beneath the upper electrode. An upper electrode may be provided with an annular outer or a solid inner heated die to melt a coating layer. Alternatively a duct may be arranged within the electrode to supply hot air to melt a coating or hot air may be supplied into a tube about the electrode. The upper electrode may have a serrated end and a cooling plate may be held by electromagnets on the upper coating layer. Roller electrodes having cutter discs may have hot air assistance to penetrate the coatings. Roller electrodes without cutter discs may each press a wire into the coating, heated by hot air, to establish initial connection. Wires of lowmelting point 170, 171, 172, Fig. 44, are arranged by adhesive tapes above, between and below the sheets 1, 2 the wires 170, 171 being connected to the lower electrode roller 164 and wires 171, 172 being connected to upper electrode roller 164. Carbon dioxide is blown from orifices 173 to prevent oxidation.